If you force everyone to use 64bit sector numbers, I don't understand how
you can claim "still working just fine on 32bit"?

64bit sector numbers work just fine on 32-bit machines.

Depends on the definition of "fine".

At some point ext4 is probably going to be the de facto standard, which very
many people want to use, because it has all the new features, which won't be
ported to ext2/3. So I still don't understand, what's so wrong about a
little tuning in both directions?

Just seems like wasted effort to me.

I disagree.
Many developer still brag about how Linux runs on about everything, but
it's little steps like this, which make it more and more a joke.

What joke? With CONFIG_LBD, 32-bit machines can already support large
block devices.

If you feel that hardcoding u64 as sector numbers will mean ext4
suddenly fails on 32-bit, you misunderstand the situation completely.